This invention relates to a method of and apparatus for fluidization and more particularly for drying bulk material.
Fluidization is employed extensively for contacting gaseous materials with solids since contacting takes place on relatively much larger surfaces when contacted solids are fluidized. Fluidization is employed for conveying purposes as well because in their fluidized state solids behave as liquids and, thus, can more easily be advanced.
Fluidization is generally obtained by having a bed of the material to be fluidized traversed by a fluidizing gaseous medium or fluid. However, various difficulties may be met with in the course of fluidization. Gas velocities needed for obtaining and maintaining fluidization are difficult to conform to values required for technological reasons as in case of drying, absorbing, chemical reactions, conveying and the like. Powder-like or minute particles of fluidized solids may deposit or flow back into inlet areas of fluidizing fluids at shut down periods and cause start-up problems. Channels may be formed in fluidized beds particles of which may be transported in the stream of withdrawing fluidizing fluids. Fluidized beds may have uneven surfaces and variable porosities both of which have adverse effects on start-ups. Homogeneous gas distribution in fluidized beds could only be obtained with beds of limited breadths.
Such difficulties could partly be overcome by fluidization methods where a fluidizing fluid of pulsating flow velocity is employed and is introduced at a plurality of level locations simultaneously. The fluidizing fluid enters through tuyeres in orifices of a distributor wherefrom it withdraws substantially transversely of the bed.
The present invention is thought to be an improvement over such methods in that a more uniform fluidization is permitted and, thereby, considerably broader beds are rendered possible without backflowing at shut-downs and start-up problems at refluidizations.